There are a few steps to set up a duplicate blog page.
1.) Duplicate template_blog.php and rename it (eg template_blog_new.php)
2.) Open up the new template_blog_new.php file and change the text:
Template Name: Blog Overview
Template Name: Blog New
3.) You need to edit the query_string to include the correct categories. Find this code:
$query_string = "cat=".$negative_cats."&paged=$paged";
and change it to:
$query_string = "cat=1,2,3,4,5&paged=$paged";
This would include categories with the ID's 1 / 2 / 3 / 4 and 5. You can find the ID's for the categories in WordPress admin, just look in the status bar for the ID number when hovering over the link to the category on the Post -> Categories page.
4.) Save and upload to your site.
5.) When you create a page you want to display this New Blog Page on, select Blog New (the name we gave the page in step 2) as the Page Template (on the right side of the page just under the Publish box).
If you have any questions about this, please let me know.